Electrolytic process for production of perfluorocyclohexane derivatives

ABSTRACT

Aromatic hydrocarbons which have undergone nuclear substitution with a trifluoromethyl group are electrolytically fluorinated in anhydrous hydrogen fluoride. The mixed gas which is consequently formed is sent through the aqueous solution of sodium sulfite containing therein potassium iodide, thereafter cooled and collected, and subjected to refining treatment such as by trapto-trap distillation, distillation, or gas chromatography to obtain perfluorocyclohexane derivatives.

iinite States atent n91 Nagase et al.

[ Mar. 18, 1975 [5 1 ELECTROLYTIC PROCESS FOR PRODUCTION or PERFLUOROCYCLOHEXANE DERIVATIVES [76] Inventors: Shunji Nagase, 13-1 Aza-Shikannonmichi-Nishi, Tashiro-cho, Chigusa-ku; Hajime Baba, 34- 140, Aza-Togasama, Ohaza-Inokoishi, Idaka-cho, Chigusa-lcu; Kazuo Kodaira, l Hirate-cho, 1 chome, Kita-ku; Takashi Abe, 34-140, Ala-Togasama, Ohaza-Inokoishi, Idakacho, Chigusa-ku; Michimasa Yonekura, 19, Shinike-cho, l chome, Chigusa-ku, all of Nagoya, Japan 22 Filed: Mar. 12, 1973 21 Appl. No.: 340,602

[30] Foreign ApplicationPriority Data June I, 1972 Japan 47-54698 [52] US. Cl. 204/59 F [5 1] Int. Cl B0lk 3/00 [58] Field of Search 204/59 F, 72, 78, 81

[56] References Cited UNITED STATES PATENTS 3,547,790 12/1970 Dannels ct al 204/59 F OTHER PUBLICATIONS Handbook of Chem. and Physics, 32nd Ed., 1950, pages 1l48-l 149, (Chemical Rubber Publishing Co).

Primary Examiner-R. L. Andrews Attorney, Agent, or Firm-Kurt Kelman [57] ABSTRACT Aromatic hydrocarbons which have undergone nuclear substitution with a trifluoromethyl group are electrolytically fluorinated in anhydrous hydrogen fluoride. The mixed gas which is consequently formed is sent through the aqueous solution of sodium sulfite containing therein potassium iodide, thereafter cooled and collected, and subjected to refining treatment such as by trap-to-trap distillation, distillation, or gas chromatography to obtain perfluorocyclohexane derivatives.

4 Claims, N0 Drawings ELECTROLYTIC PROCESS FOR PRODUCTION OF PERFLUOROCYCLOHEXANE DERIVATIVES BACKGROUND OF THE INVENTION This invention relates to a novel process for the production of trifluoromethyl-substituted perfluorocyclohexane derivatives.

Perfluorocycloalkanes obtained in consequence of complete substitution of hydrogen atoms with fluorine atoms are non-flammable and show unusually high chemical stability. Because of these properties, they are extensively used as coolants, solvents, diluents, etc.

One of the methods heretofore disclosed as being useful for the production of perfluorocycloalkanes is such that corresponding aliphatic hydrocarbons or aromatic hydrocarbons are fluorinated with fluorine gas or with a metal fluoride (such as, for example, cobalt trifluoride or silver difluoride). In the case of the production resorting to electrolytic fluorination, a method whereby partially fluorinated alicyclic hydrocarbons are fluorinated has been known to the art (German Pat. No. 1,119,262). It is universally known that, when aromatic hydrocarbons are directly subjected to electrolytic fluorination, the desired results are not obtained because the electrolysis produces tarry substances which adhere to the surface of electrodes in use and consequently interfere with further passage of electrons.

It is a primary object of this invention to provide a process for the production of perfluorocycloalkanes by efficient electrolytic fluorination of aromatic hydrocarbons.

SUMMARY OF THE INVENTION To accomplish the aforementioned object, the process according to the present invention effects the production of perfluorocyclohexane derivatives by directly subjecting to electrolytic fluorination, in anhydrous hydrogen fluoride, aromatic hydrocarbons which have undergone nuclear substitution with a trifluoromethyl group.

The resultant product of fluorination contains fluorinated hydrocarbons and traces of oxygen difluoride, etc. besides the corresponding perfluorocyclohexane derivatives. The perfluorocyclohexane derivatives aimed at by this invention can be obtained from this mixture by scrubbing the mixture with the aqueous solution of sodium sulfite containing a small proportion of potassium iodide to remove therefrom oxygen difluoride and stripping the residual mixture of fluorinated hydrocarbons by means of trap-to-trap distillation, gas chromatography or some other device.

DETAILED DESCRIPTION OF THE INVENTION The inventors continued a devoted study with a view to developing a process for producing perfluorocycloalkanes at a high efficiency by direct electrolytic fluorination of aromatic hydrocarbons. As a consequence, they have made the unexpected discovery that, when the electrolytic fluorination is performed on aromatic hydrocarbons which have in advance been subjected to nuclear substitution with a trifluoromethyl group, the reaction proceeds smoothly without entailing the evolution of tarry substances. They have accomplished the present invention on the basis of this discovery.

To be more specific, trifluoromethyl-Snbstituted perfluorocyclohexane derivatives can easily be obtained by subjecting to electrolytic fluorination, in anhydrous hydrogen fluoride, benzene derivatives which have undergone nuclear substitution with at least one trihalogenomethyl group.

Examples of the benzene derivatives which have undergone nuclear substitution with at least one trihalogenomethyl group and which are usable as raw materials for the present invention include benzotrichloride and other similar benzene derivatives which have such trihalogenomethyl groups as are convertible into trifluoromethyl groups in anhydrous hydrogen fluoride as well as benzene derivatives such as benzotrifluoride and bis-(trifluoromethyl)-benzenes which have undergone nuclear substitution with a trifluoromethyl group. These benzene derivatives may possess additional halogen atoms as nuclear substitution groups. In cases where the nuclear substitution group is halogen atoms excluding fluorine atom, a part of them are sometimes replaced with fluorine atoms in consequence of the electrolytic fluorination.

The electrolytic fluorination of the present invention is effected by dissolving the compound selected as the raw material in anhydrous hydrogen fluoride, immersing in the resultant solution paired nickel electrodes and energizing the electrolytic system. Desirably, the electrolytic bath is maintained at temperatures between l0 and +20C. A bath temperature exceeding the upper limit of +20C is not desirable because at such temperature, anhydrous hydrogen fluoride boils and undergoes vaporization. Generally, the voltage is selected in the range between 4 and 9 V and the anode current density in the range between 0.5 and 4.0 A/dm Optionally, the electrolytic bath may incorporate therein the fluoride of alkali-metal or alkaline earth metal as an agent for enhancing electroconductivity. The suitable amount of this agent is on the order of 10 g per liter of anhydrous hydrogen fluoride. During the electrolysis, an inert gas such as helium or nitrogen may be blown into the bath in the form of finely divided bubbles for the purpose of heightening the stirring effect of the hydrogen fluoride solution promoting the elimination of the heat of reaction and facilitating the liberation of the vaporized fluorination product from the bath. By this introduction of the inert gas, even a reaction product having a fairly high boiling point can be vaporized and collected.

This electrolytic treatment gives birth to a mixture consisting of perfluorocyclohexane derivatives, other fluorinated hydrocarbons, traces of oxygen difluoride and other components. Of these components, oxygen difluoride is removed by scrubbing the mixture with the aqueous solution of sodium sulfite containing a small proportion of potasium iodide. The perfluorocyclohexane derivatives, other fluorinated hydrocarbons and the like are collected in a trap kept cool with ice and liquefied nitrogen and thereafter separated by means of trap-to-trap distillation, gas chromatography or some other device. If the resultant product of electrolytic treatment has a very high boiling point and remains unvaporized, then it settles to the bottom of the electrolytic bath. The product which has gathered on the bottom may be withdrawn through a drain cock provided at the bottom of the cell, stripped of hydrogen fluoride by the treatment using the aqueous solution of an alkali, further freed of moisture content with anhydrous sodium sulfate added thereto, and thereafter refined as by distillation to obtain the desired derivatives.

The identity of the products obtained by the present invention has been ascertained by the test resorting to infrared absorption spectroscopy, mass spectroscopy, etc.

The raw materials to be used for the process of this invention, i.e., anhydrous hydrogen fluoride and halogenomethyl benzene derivatives are invariably easy of handling and obtainable at low prices. The process itself can be carried out with a very simple device. The amount of electricity and that of fluorine are both small. Consequently, the process of this invention can be practiced easily on a commercial scale.

Now, the present invention is described with reference to preferred embodiments, which are intended solely to be illustrative of the invention and not in any way liminative thereof.

Example 1 A cylindrical electrolytic cell having a volume of 1.28 liters and made of Monel Metal was used as the reaction vessel. Nine nickel-plate anodes and ten nickelplate cathodes were arranged alternately within the cell and a bubbler made of polytetrafluoroethylene fiber was placed on the bottom of the cell. The said electrodes had an equal effective area of 20 dm The top of this electrolytic cell was extended and connected to a tube packed with sodium fluoride via a copper-made reflux condenser cooked with brine at C.

In the electrolytic cell of the construction just mentioned, 1.28 liters of anhydrous hydrogen fluoride was introduced and deprived of traces of impurities by preliminary electrolysis. Thereafter, benzotrifluoride was continuously introduced portionwise into the electrolytic cell by means of a micro-pump to effect electrolytic fluorination under conditions of anode current density of 0.9 1.4 A/dm bath voltage of 5.5 5.8 V and bath temperature of 5- 7C. The total amount of benzotrifluoride used in the electrolysis was 28.8 g (0.197 ml). During the reaction, helium was continuously blown into the electrolytic bath at a flow rate of 150 ml/min. via the bubbler disposed on the bottom of the electrolytic cell.

The gas which evolved from the electrolytic bath was led through the tube packed with sodium fluoride to the traps cooked with ice and liquefied nitrogen. l-lydro'gen was allowed to escape into the atmosphere. The total amount of electricity used ,in the electrolysis was 129 A. hours. After completion of the electrolysis, the blowing of helium into the bath was continued for 1.5 hours to forward the portion of product still remaining in the bath and in the sodium fluoride tube to the cooled traps.

From the collected fluorocarbons, 24.0 g of trifluoromethylundecafluorocyclohexane and 8.2 g of 1,2-bis- (trifluoromethyl)-octafluorocyclopentane were obtained by means of trap-to-trap distillation and gas chromatography. The combined yield of perfluoro-C cyclo-compounds was found to be 46.7 percent. Other products were C C fluorocarbons.

Example 2 Electrolytic fluorination was conducted on 28.9 g (0.197 mol) of benzotifluoride by faithfully repeating the procedure of Example 1, except that 10 g of sodium fluoride was incorporated as an additive to the electrolytic bath.

A total of 43.1 g of fluorocarbons were collected in the cooled traps and they were refined by trap-to-trap distillation and gas chromatography. Consequently, there were obtained 33.0 g of trifluoromethylundecafluorocyclohexane and 4.2 g of 1,2-bis- (trifluoromethyl)-octafluorocyclopentane. The combined yield of these perfluoro-C -cyclo-compounds was 53.5%. Other products were C, C fluorocarbons.

Example 3 By following substantially the same procedure as that of Example 1, p-chlorobenzotrifluoride was subjected to electrolytic fluorination. The conditions for the electrolysis were anode current density of 1.1 1.5 A/dm bath voltage of 5.5 5.9 V and bath temperature of 7 8C. The total amount of p-chlorobenzotrifluoride was 36.7 g (0.203 mol) and the amount of electricity consumed was A. hours.

From the collected fluorocarbons weighing 22.6 g, there were obtained 11.8 g of trifluoromethylundecafluorocyclohexane, 7.0 g of l-trifluoromethyl-4-chlorodecafluorocyclohexane and 1.0 g of l,2-bis- (trifluoromethyl)-octafluorocyclopentane. The combined yield of these perfluoro-C -cyclo-compounds was 27.1 percent. Other products were C C fluorocarbons.

What is claimed is:

l. A process for the production of perfluorocyclohexane derivatives which comprises, dissolving nuclear substituted benzene consisting of benzene substituted by one to six trihalogenomethyl groups in anhydrous hydrogen fluoride, immersing a pair of electrodes in the resultant solution, electrolizing the said resultant solution at a temperature in the range between -10C and +20C, a voltage in the range between 4V and 9V, and an anode current density in the range between 0.5 A/dm and 4.0 A/dm and recovering trifluoromethylsubstituted perfluorocyclohexane derivatives.

' 2. The process according to claim 1 wherein the said resultant solution is electrolized while an inert gas is blown thereinto.

3. The process according to claim 1 wherein the electrolized solution contains a member selected from the group consisting of benzotrifluoride, bis(trifluoromethyl) benzene, and p-chlorobenzotrifluoride.

4. The process according to claim 1 wherein the recovered trifluoromethyl-substituted perfluorocyclohexane derivatives are selected from the group consisting of trifluoromethylundecafluorocyclohexane, 1,- 2-bis-(trifluoromethyl)-octafluorocyclo-pentane, and

l-trifluoromethyl-4-chlorodecafluorocyclohexane. 

1. A process for the production of perfluorocyclohexane derivatives which comprises, dissolving nuclear substituted benzene consisting of benzene substituted by one to six trihalogenomethyl groups in anhydrous hydrogen fluoride, immersing a pair of electrodes in the resultant solution, electrolizing the said resultant solution at a temperature in the range between -10*C and +20*C, a voltage in the range between 4V and 9V, and an anode current density in the range between 0.5 A/dm2 and 4.0 A/dm2, and recovering trifluoromethyl-substituted perfluorocyclohexane derivatives.
 2. The process according to claim 1 wherein the said resultant solution is electrolized while an inert gas is blown thereinto.
 3. THE PROCESS ACCORDING TO CLAIM 1 WHEREIN THE ELECTROLIZED SOLUTION CONTAINS A MEMBER SELECTED FROM THE GROUP CONSISTING OF BENZOTRIFLUORIDE, BIS(TRIFLUOROMETHYL) BENZENE, AND PCHLOROBENZOTRIFLUORIDE.
 4. The process according to claim 1 wherein the recovered trifluoromethyl-substituted perfluorocyclohexane derivatives are selected from the group consisting of trifluoromethylundecafluorocyclohexane, 1,2-bis-(trifluoromethyl)-octafluorocyclo-pentane, and 1-trifluoromethyl-4-chlorodecafluorocyclohexane. 